Jet pump



Sept. 23, 1958 E. P. NEUMANN ETAL JET PUMP Filed July 50, 1953 Fig. I

Fig. 3

EXPANSION VALVE BOILER 3o 30 I 0 58 EVAPORATOR .O

CoNDENsER- g t SEPARATOR LEI INVENTORS ERNEST P. NEUMANN FERDINAND LUSTWERK MI W, ATTORNEYS United States atent fitice.

2,852,922 Patented Sept. 23, 1958 JET PUMP Ernest P. Neumann and Ferdinand Lustwerk, Lincoln,

Mass., assignors, by mesne assignments, to Rheem Manufacturing Company, a corporation of California Application July 30, 1953, Serial No. 371,397

3 Claims. (Cl. 62-500) The present invention relates to jet pumps of the type conventionally employed to cause a pressurized stream of gas or vapor to entrain another gas or gas containing liquid droplets and thereby move it through a conduit.

The primary object of the present invention is to improve the efliciency with which jet pumps may be operated. That is to say, we have as an overall goal a significant increase in the amount of work done in terms of the energy applied to the system.

An important feature of our invention resides in the provision of at least one secondary nozzle disposed adjacent the primary nozzle and mounted in position to direct a stream into the mixing tube. By introducing into the secondary nozzle a coolant, we succeed in cooling the fluid mixture in the mixing tube and thereby bring about an increase in discharge pressure of as much as fifty percent.

It is impossible, at least at this time, to explain the phenomena involved, but experimental results definitely reveal the striking and unexpected increase in efficiency.

Another feature of the invention resides in employing as a coolant a liquid characterized by a relatively high latent heat of vaporization. Such a liquid absorbs proportionately larger amounts of heat and therefore is more effective, since at least some portion of the coolant is vaporized in the mixing tube. From this it follows that a limitation upon the operation of a jet pump in accordance with our invention is that the temperature of the gases must be high enough to vaporize some of the cooling liquid injected; it goes without saying that our invention is useful only in systems where a gas is used to pump either another gas or a mixture of gas and liquid droplets and not to the relatively rare system in which one liquid is used to pump another.

Although our invention may be advantageously em ployed for a wide variety of purposes, we have found it particularly useful in connection with a jet pump refrigeration system in which hot pressurized vapor from a boiler is forced through a jet pump and utilized to entrain refrigerant vapors from an evaporator, the pressurized mixture thus being forced into a condenser from which the mixture of liquids passes to a separator for subsequent recycling. In such an installation the coolant may take the form of the condensed refrigerant piped to the jet from a bleeder line connected to the separator.

These and other objects and features of the invention will be more readily understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawing in which:

Fig. 1 is a longitudinal cross section of a jet pump constructed in accordance with the invention,

Fig. 2 is a view in end elevation of the nozzle end of the jet pump, and

Fig. 3 is a schematic view illustrating the invention as embodied in a jet pump refrigeration system.

As shown in Fig. 1 the jet pump includes an entrance chamber provided with an inlet duct 12 in one of the p side walls and a primary nozzle 14 set in an end wall 13. Received in an aperture in the opposite end wall is the mouth portion 16 of a mixing tube 18 which merges into a restricted throat portion 20 which in turn merges into a diffuser portion 22 having a diverging bore. Mounted in the end wall 13 of the entrance chamber 10 are three secondary nozzles 30 arranged symmetrically and coaxially about the primary nozzle 14 and so positioned that their discharge ends terminate at the mouth 16 of the mixing tube 18, the three nozzles 30 being disposed in converging relation and thereby positioned to direct streams of fluid into the mixing tube 18.

It will be recognized that the jet pump thus far described is conventional with the exception of three nozzles 30. It should also be pointed out, however, that the throat 20 should be of smaller diameter than would be selected for a conventional jet pump. For a discussion of jet pumps and the designed considerations applicable thereto, reference is made to An investigation of ejector design by analysis and experiment appearing in the September 1950 issue of Journal of Applied Mechanics at page 299.

If the nozzle 14 be connected to a source of pressurized heated gas or vapor and the duct 12 connected to a supply of gas or a mixture of gas and liquid droplets, the flow of vapor through the nozzle 14 will entrain gas or gasliquid mixture through the chamber and the duct 12, the two fluids being mixed in the mixing tube 18 and then passed through the restricted throat 2t and discharged through the diffuser 22.

If now the nozzles 30 be connected to a source of liquid having a dew point lower than the stagnation temperature in the mixing tube 13, it will be observed that the pressure at the discharge end of the diffuser will show a marked rise, and the quantity of fluid pumped through the duct 12 will increase correspondingly. In other words, the pumping rate is greatly increased.

Although the explanation is not clear, it does seem evident that the increased efficiency of the jet pump is the result of cooling the fluid stream in the mixing tube. Although an improvement may be noted it but one nozzle Tall is employed, we have achieved improved performance with a plurality of nozzles disposed symmetrically about the axis of the nozzle 14, and three such nozzles appear to be optimum.

As against a jet pump lacking any cooling means, an improvement in efliciency of perhaps ten percent may be achieved by surrounding the mixing tube and restricted orifice with radiating cooling fins, and that increase can be raised to twenty-five percent by passing liquid air over the cooling fins. However, as opposed to these methods of cooling, we have achieved an increase in efliciency of fifty percent by adopting the simple construction shown, particularly When the fluid used as the coolant is characterized by a high latent heat of vaporization.

In Fig. 3 we have shown a jet pump refrigeration sys tem constructed in accordance with the present invention. in this system one fluid is vaporized in a boiler $0 and passed to the primary nozzle 14 of the jet pump. The conduit 12 is connected to a conventional evaporator so that the jet pump serves to pump vaporized refrigerant from the evaporator to a condenser 52 where the mixture of boiler fluid and refrigerant fluid is condensed. From the condenser 52 the mixture of fluids passes to a gravity separator 54. The boiler fluid, being lighter, goes to he top of the separator from where it is pumped back into the boiler by means of a pump 56. The heavier refrigerant fluid goes to the bottom of the separator and thence returns to the evaporator through a conventional expansion valve 58. A conduit 60, of relatively small diameter, is provided to take condensed refrigerant fluid from the line serving the evaporator to the nozzles 30.

In a system of this sort the coefficient of performance will be fifty percent higher than one in which the special jet pump of our invention is replaced by one of conventional design.

It is important to note that the performance of a jet pump constructed in accordance with our invention is slightly better if the pump is arranged in vertical position with the nozzles 30 pointing downward, since better mixing is achieved by that disposition.

Having thus disclosed our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus of the character described comprising a jet pump including an entrance chamber having an inlet duct for fluid to be pumped, a primary nozzle mounted in said chamber, a mixing tube providing discharge from said chamber disposed in alignment with said primary nozzle, a diffuser connected to the discharge end of said mixing tube, and a boiler for supplying hot propellant vapors to said primary nozzle, a secondary nozzle adjament said primary nozzle in general alignment with said mixing tube and a container for a coolant liquid connected to said secondary nozzle, passage of said coolant liquid through said secondary nozzle being motivated by passage of said vapors through said primary nozzle whereby said fluid, vapor and liquid will pass through said mixing tube.

2. In a pumping process including the steps of passing hot propellant vapors through a primary nozzle and into a mixing tube and difliuser and thereby entraining fluid to be pumped in the mixing tube and diffuser; the improvement which comprises the step of directing into the mixing tube substantially immediately adjacent the hot vapor inlet thereto a stream of coolant liquid in addition to the propellant vapors and fluid to be pumped.

3. In a refrigeration system employing a boiler for feeding hot propellant vapors through a jet pump to compress refrigerant vapors from an evaporator and pump them to the condenser, said propellant vapors being passed through a primary nozzle and into a mixing tube and diffuser and thereby entraining the refrigerant vapors in the mixing tube and diffuser, the improvement which comprises directing-into the mixing tube substantially immediately adjacent the entry of said hot vapors into said mixing tube a stream of condensed refrigerant liquid in addition to the propellant vapors and refrigerant vapors.

References Cited in the file of this patent UNITED STATES PATENTS 

